The physical therapy table of the invention has been designed for use with the McKenzie technique, a passive exercise for treatment of spinal problems, but may be used for many other physical therapy purposes such as massage, stretching and muscle-energy techniques.
The spinal column is made of vertebrae and discs. Movement of the spine takes place at the disc, which is a soft deformable tissue. The disc is shaped like a jelly doughnut wherein the jelly center is the nucleus and the dough portion is a thick fibrous wall called the annulus. When a person bends forward (flexion), the anterior or front part of the disc is compressed, the posterior or back part of the disc expands and the nucleus is pushed posteriorly against the annulus. The opposite happens with a backward bend (extension): the posterior part of the disc is compressed, the anterior part expands and the nucleus moves anteriorly. The same type of disc deformation with nucleus movement also happens in side bending. In a normal disc, the nucleus returns to it's central position when the spine returns to a neutral resting posture.
With flexion of the lumbar spine and the associated compression of the anterior nucleus, the pressure within the disc increases dramatically and this increased pressure is directed against the posterior wall. Many people maintain a flexed sitting posture in the lumbar region for sustained periods every day. They sleep in a flexed posture, sit or bend over to dress, sit to drive a car to work and sit at work and at meals. At the end of the day, they sit in a recliner to relax. Most daily routines require a great deal of flexion but almost no extension to counter the effects of this flexion.
When the flexed posture is maintained for most of the time, the nucleus accumulates on the back wall of the disc. Months and years of flexion without extension causes the anterior annulus to shorten. Extension becomes uncomfortable and the full extension range of motion is lost. This is called extension dysfunction.
With prolonged or repeated flexion, the posterior annulus becomes over stretched and weakened and, with continued high pressure from the nucleus, it begins to bulge. As it bulges (deforms) low back pain is felt. At some point in the process, the pressure from the nucleus is sufficient to begin breaking through the inner layers of the posterior annulus. By the time this fissuring has broken through to the middle layers of the annulus, the patient is reporting constant and severe low back pain. This mechanical deformation of the disc which remains when we return to a normal resting position and the possible annulus damage is called posterior disc derangement.